Permanent magnet, motor, and generator

ABSTRACT

A permanent magnet includes: a composition expressed by a composition formula: R p Fe q M r Cu t Co 100-p-q-r-t  (R is at least one element selected from rare-earth elements, M is at least one element selected from Zr, Ti, and Hf, 10.5≦p≦12.5 at %, 23≦q≦40 at %, 0.88≦r≦4.5 at %, 4.5≦t≦10.7 at %); and a metal structure containing a Th 2 Zn 17  crystal phase and a Cu-rich phase having a Cu concentration higher than that of the Th 2 Zn 17  crystal phase. In a cross section including a c-axis of the Th 2 Zn 17  crystal phase, a number of intersections of the Cu-rich phases existing in an area of 1 μm square is 10 or more.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of prior International ApplicationNo. PCT/JP2013/005462 filed on Sep. 13, 2013; the entire contents of allof which are incorporated herein by reference.

FIELD

Embodiments described herein generally relate to a permanent magnet, amotor, and a power generator.

BACKGROUND

As examples of a high-performance rare-earth magnet, a Sm—Co-basedmagnet and a Nd—Fe—B-based magnet and so on are known. In these magnets,Fe and Co contribute to an increase in saturation magnetization.Further, in theses magnets, rare-earth elements such as Nd and Sm arecontained to bring about large magnetic anisotropy resulting frombehaviors of 4f electrons of the rare-earth elements in a crystal field.This makes it possible to obtain a high coercive force and realize thehigh-performance magnet.

Such a high-performance magnet is mainly used in electric devices suchas motors, speakers, and measuring instruments. There is an increasingdemand for a reduction in weight and a reduction in power consumption ofvarious kinds of electric devices, and in order to cope with this, thereis a demand for a higher-performance permanent magnet whose maximummagnetic energy product (BHmax) is improved. In recent years, a variablemagnetic flux motor has been proposed and contributes to an increase inefficiency of the motor.

The Sm—Co-based magnet has a high Curie temperature and thus can realizean excellent motor property at high temperature, but there is a demandfor a higher coercive force, higher magnetization, and improvement insquareness ratio. In order for higher magnetization of the Sm—Co-basedmagnet, increasing the Fe concentration is considered to be effective,but the squareness ratio tends to decrease due to increasing the Feconcentration in manufacturing methods in prior arts. In order torealize a high-performance magnet for motor, a technique of enabling anexcellent squareness ratio while improving the magnetization in acomposition with a high Fe concentration is requested.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a view showing an example of a bright-field image by a TEM.

FIG. 2 is a view showing an example of a mapping result by a TEM-EDX.

FIG. 3 is a view illustrating a permanent magnet motor.

FIG. 4 is a view illustrating a variable magnetic flux motor.

FIG. 5 is a view illustrating a power generator.

DETAILED DESCRIPTION

A permanent magnet in an embodiment includes: a composition expressed bya composition formula: R_(p)Fe_(q)M_(r)Cu_(t)Co_(100-p-q-r-t), where Ris at least one element selected from the group consisting of rare-earthelements, M is at least one element selected from the group consistingof Zr, Ti, and Hf, p is a number satisfying 10.5≦p≦12.5 at %, q is anumber satisfying 23≦q≦40 at %, r is a number satisfying 0.88≦r≦4.5 at%, and t is a number satisfying 4.5≦t≦10.7 at %; and a metal structurecontaining a Th₂Zn₁₇ crystal phase and a Cu-rich phase having a Cuconcentration higher than that of the Th₂Zn₁₇ crystal phase. In a crosssection including a c-axis in the Th₂Zn₁₇ crystal phase, a number ofintersections of the Cu-rich phases existing in an area of 1 μm squareis 10 or more.

First Embodiment

A permanent magnet in an embodiment will be described below.

<Configuration Example of Permanent Magnet>

A permanent magnet in this embodiment includes a composition expressedby a composition formula: R_(p)Fe_(q)M_(r)Cu_(t)Co_(100-p-q-r-t), whereR is at least one element selected from rare-earth elements, M is atleast one element selected from Zr, Ti, and Hf, p is a number satisfying10.5≦p≦12.5 at %, q is a number satisfying 23≦q≦40 at %, r is a numbersatisfying 0.88≦r≦4.5 at %, and t is a number satisfying 4.5≦t≦10.7 at%.

The element R in the above composition formula is an element that canbring about large magnetic anisotropy in the magnet material. As theelement R, one or more elements selected from rare-earth elementsincluding yttrium (Y) can be used and, for example, samarium (Sm),cerium (Ce), neodymium (Nd), and praseodymium (Pr) and the like can beused and, in particular, use of Sm is desirable. For example, in thecase where a plurality of elements including Sm are used as the elementR, setting the concentration of Sm to 50 at % or more of the wholeelements applicable as the element R makes it possible to increaseperformance of the magnet material such as a coercive force.

It is more preferable to set the concentration of Sm to 70 at % or moreof the elements applicable as the element R. Any of the elementsapplicable as the element R brings about large magnetic anisotropy inthe magnet material, and setting the concentration of the elementsapplicable as the element R to 10.5 at % or more and 12.5 at % or lessmakes it possible to increase the coercive force. When the concentrationof the elements applicable as the element R is less than 10.5 at %, alarge amount of α-Fe precipitates to decrease the coercive force,whereas when the concentration of the elements applicable as the elementR exceeds 12.5 at %, saturation magnetization decreases. Theconcentration of the elements applicable as the element R is preferably10.7 at % or more and 12.3 at % or less, and more preferably 10.9 at %or more and 12.1 at % or less.

M in the above composition formula is an element for enabling a highcoercive force to be exhibited in a composition with a high Feconcentration. As the element M, for example, one or more elementsselected from titanium (Ti), zirconium (Zr), and hafnium (Hf) is/areused. When the content r of the element M is 4.5 at % or more, ahetero-phase excessively containing the element M is likely to begenerated, and both the coercive force and magnetization are likely todecrease. When the content r of the element M is less than 0.88 at %,the effect of increasing the Fe concentration is likely to decrease. Inother words, the content r of the element M is preferably 0.88 at % ormore and 4.5 at % or less. Further, the content r of the element M ispreferably 1.14 at % or more and 3.58 at % or less, and more preferably1.49 at % or more and 2.24 at % or less.

The element M may be any one of Ti, Zr, Hf and preferably contains atleast Zr. Especially when 50 at % or more of the element M is Zr, it ispossible to increase the coercive force of the permanent magnet. On theother hand, Hf in the element M is particularly expensive, and thus evenwhen Hf is used, the amount of Hf used is preferably small. For example,the content of Hf is preferably less than 20 at % of the element M.

Cu is an element for enabling a high coercive force to be exhibited inthe magnet material. The content of Cu is preferably 3.5 at % or moreand 10.7 at % or less. When a larger amount of Cu is compounded, adecrease in magnetization is significant, whereas when a smaller amountof Cu is compounded, it becomes difficult to obtain a high coerciveforce and an excellent squareness ratio. The content t of Cu ispreferably 3.9 at % or more and 9.0 at % or less, and more preferably4.3 at % or more and 5.8 at % or less.

Fe is an element mainly responsible for magnetization of the magnetmaterial. When a large amount of Fe is compounded, saturationmagnetization of the magnet material can be increased. However, when Feis compounded too much, precipitation of α-Fe and phase separation makeit difficult to obtain a desired crystal phase, and may decrease thecoercive force. Accordingly, the content q of Fe is preferably 23 at %or more and 40 at % or less. The content q of Fe is more preferably 26at % or more and 36 at % or less, and still more preferably 29 at % ormore and 34 at % or less.

Co is an element responsible for magnetization of the magnet materialand for enabling a high coercive force to be exhibited. Moreover, when alarge amount of Co is compounded, a high Curie temperature can beobtained, so that Co also has a function of improving thermal stabilityof the magnet property. When the compounding amount of Co is small,these effects are likely to decrease. However, when Co is added toomuch, the ratio of Fe relatively decreases and may decrease themagnetization. For example, substituting Ni, V, Cr, Mn, Al, Si, Ga, Nb,Ta, W for 20 at % or less of Co can improve the magnet property such asthe coercive force. However, excessive substitution may decrease themagnetization, and therefore the substitution amount is preferably 20 at% or less of Co.

The permanent magnet in this embodiment further includes a metalstructure including a plurality of hexagonal Th₂Zn₁₇ crystal phases(2-17 crystal phases) and a plurality of Cu-rich phases higher in Cuconcentration than the Th₂Zn₁₇ crystal phases.

A Sm—Co-based magnet generally includes, in its sectional structure, atwo-dimensional metal structure including a cell phase of the Th₂Zn₁₇crystal phase (2-17 phase) and a cell wall phase of a hexagonal CaCu₅crystal phase (1-5 crystal phase). For example, the cell wall phase isone of the Cu-rich phases and is a grain boundary phase existing at agrain boundary of the cell phase, and the plurality of cell phases arepartitioned by the cell wall phase. The above structure is also called acell structure.

The Cu-rich phase is a phase higher in Cu concentration than the Th₂Zn₁₇crystal phase. Preferably, the Cu concentration in the Cu-rich phase ishigher than the Cu concentration in the Th₂Zn₁₇ crystal phase and is,for example, 30 at % or more. The Cu-rich phase exists in a linear shapeor plate shape in the cross section including the c-axis in the Th₂Zn₁₇crystal phase. The structure of the Cu-rich phase is not particularlylimited but, for example, a hexagonal CaCu₅ crystal phase (1-5 crystalphase) can be exemplified. Further, the permanent magnet in thisembodiment may include a plurality of Cu-rich phases different in phase.

In this embodiment, the observation of the metal structure such as theTh₂Zn₁₇ crystal phase and the Cu-rich phase is recognized as follows forinstance. First, observation of a sample under a transmission electronmicroscope (TEM). The sample used in the above observation is a sampleafter a main aging treatment. At this time, the sample is preferably anunmagnetized article.

The concentration of each element in the Th₂Zn₁₇ crystal phase and theCu-rich phase can be measured using, for example, a TEM-energydispersive X-ray spectroscopy (TEM-EDX). The TEM observation isperformed with, for example, a 200 k-fold magnification. In thisembodiment, a cross section including the c-axis in the Th₂Zn₁₇ crystalphase is observed.

For measurement of the concentration of each element in each phase, inparticular, a phase such as a cell wall between cell phases, a3-dimensional atom probe (3DAP) is preferably used. In the case ofanalysis by the TEM-EDX, even if the phase between the cell phases isobserved, it may be impossible to accurately measure the concentrationof each element in the phase between the cell phases because atransmission electron beam is transmitted through both of the cell wallphase and the cell phase. For example, the Sm concentration or the likesometimes becomes slightly higher (about 1.2 times to about 1.5 timesthe measurement value by the 3DAP).

The measurement of the concentration of the element in each phase by the3DAP is performed in the following procedure. First, the sample isthinned by dicing, and from the thinned sample, a needle-shaped samplefor pickup atom probe (AP) is fabricated by a focused iron beam (FIB).Based on plane spacing (about 0.4 nm) of atomic planes (0003) of theTh₂Zn₁₇ crystal phase parallel to a phase (M-rich phase) in a plateshape rich in the element M such as Zr or the like generated verticallyto the c-axis in the Th₂Zn₁₇ crystal phase, an atom map is created.Regarding atom probe data thus created, a profile of only Cu is created,and a place where Cu is thickened is specified. This site rich in Cucorresponds to the Cu-rich phase.

A Cu concentration profile is analyzed in a direction vertical to theCu-rich phase. An analysis range of the concentration profile ispreferably 10 nm×10 nm×10 nm or 5 nm×5 nm×10 nm. A highest value (PCu)of the Cu concentration is found from the Cu concentration profileobtained by the analysis. Such measurement is conducted at 20 points inthe same sample from the Cu concentration profile, and an average valueof measurements is defined as the Cu concentration.

The measurement by the TEM-EDX or the 3DAP is conducted for an interiorportion of a sintered compact. The measurement of the interior portionof the sintered compact means as follows. First, the composition ismeasured at a surface portion and an interior portion of a cross sectioncut at a middle portion of the longest side in a surface having thelargest area, vertically to the side (vertically to a tangent of themiddle portion in the case of a curve). As for measurement points, firstreference lines that are drawn from ½ positions of respective sides inthe aforesaid cross section as starting points up to end portions towardan inner side vertically to the sides, and second reference lines thatare drawn from the middles of respective corner portions as startingpoints up to end portions toward the inner side at ½ positions ofinterior angles of the corner portions, are provided. Then, positions of1% of the lengths of the reference lines from the starting points ofthese first reference lines and the second reference lines are definedas the surface portion, and positions of 40% thereof are defined as theinterior portion. Note that when the corner portion has a curvaturebecause of chamfering or the like, the intersection of extensions ofadjacent sides is defined as end portions of the sides (middle of thecorner portion). In this case, the measurement point is a position notfrom the intersection but from portions in contact with the referencelines.

When the measurement points are set as above, in the case where thecross section is, for example, a quadrangle, the number of the referencelines is totally eight composed of the four first reference lines andthe four second reference lines, and the number of the measurementpoints is eight in each of the surface portion and the interior portion.In this embodiment, the eight points in each of the surface portions andthe interior portion all preferably are within the aforesaid compositionrange, but at least four points or more in each of the surface portionand the interior portion only need to be within the aforesaidcomposition range. This case does not define the relation between thesurface portion and the interior portion at one reference line. Theobservation is conducted after an observation surface of the interiorportion of the sintered compact thus defined is smoothed by polishing.For example, the observation points by the TEM-EDX are arbitrary 20points in the cell phase and the Cu-rich phase, and an average value ofmeasurement values obtained by excluding the maximum value and theminimum value from the measurement values at these points is found, andthis average value is set as the concentration of each element. Thisalso applies to the measurement by the 3DAP.

In the measurement result of the concentration in the Cu-rich phaseusing the above-described 3DAP, the concentration profile of Cu in theCu-rich phase is preferably shaper. Concretely, a full width at halfmaximum (FWHM) of the concentration profile of Cu is preferably 5 nm orless and, in such a case, a higher coercive force can be obtained. Thisis because when the distribution of Cu in the Cu-rich phase is sharp, adifference in domain wall energy sharply occurs between the cell phaseand the Cu-rich phase and the domain wall becomes more likely to bepinned.

The full width at half maximum (FWHM) of the concentration profile of Cuin the Cu-rich phase is found as follows. The highest value (PCu) of theCu concentration is found from the Cu profile by the 3DAP on the basisof the above-described method, and a width of a peak whose value is halfthe aforesaid value (PCu/2), namely, the full width at half maximum(FWHM) is found. Such measurement is conducted for ten peaks, and anaverage value of the values is defined as the full width at half maximum(FWHM) of the Cu profile. When the full width at half maximum (FWHM) ofthe Cu profile is 3 nm or less, the effect of improving the coerciveforce is further improved, and when it is 2 nm or less, a higher effectof improving the coercive force can be obtained.

An example of a bright-field image obtained by observation of the crosssection including the c-axis of the Th₂Zn₁₇ crystal phase by the TEM isillustrated in FIG. 1. Portions with arrows illustrated in FIG. 1 arethe Cu-rich phases.

Further, an example of a mapping result by the TEM-EDX is illustrated inFIG. 2. In FIG. 2, a portion whose longitudinal direction extends in onedirection in a white plate-shape region is regarded as one Cu-richphase.

The domain wall energy of the Cu-rich phase is higher than the domainwall energy of the Th₂Zn₁₇ crystal phase, and the difference in domainwall energy becomes a barrier of domain wall displacement. Morespecifically, the Cu-rich phase functions as a pinning site and therebycan suppress the domain wall displacement between the plurality of cellphases. This is also called a domain wall pinning effect.

In the Sm—Co-based magnet containing 23 at % or more Fe, the Cuconcentration in the Cu-rich phase is preferably 30 at % or more. In theregion where the Fe concentration is high, the Cu concentration in theCu-rich phase become more likely to vary and, for example, a Cu-richphase having a high domain wall pinning effect and a Cu-rich phasehaving a low domain wall pinning effect are generated and likely tocause a decrease in coercive force and squareness ratio. The Cuconcentration is more preferably 35 at % or more, and still morepreferably 40 at % or more.

When the domain wall leaving the pinning site is displaced, themagnetization is reversed by the amount of the displacement andtherefore decreases. If the domain walls leave the pinning sites all atonce with a certain magnetic field at the time when an external magneticfield is applied, the magnetization does not decrease with respect tothe application of the magnetic field due to application of a magneticfield at a midpoint, resulting in an excellent squareness ratio. Inother words, it is considered that at the time when a magnetic field isapplied, if the domain wall leaves the pinning site and is displacedwith a magnetic field lower than the coercive force, the magnetizationdecreases by the amount of the displacement to lead to deterioration insquareness ratio. To suppress the deterioration in squareness ratio, itis considered to be important to increase the domain wall pinning effectand, even if the domain wall leaves a pinning site, to perform pining ofthe domain wall again at another pinning site so as toe the region wherethe magnetization is reversed.

There is a case where even though the Cu-rich phases being pinning sitesare densely generated in order to perform pinning for the domain wallleaving a certain pinning site by another pinning site, the squarenessratio is not improved. Further, there is a phenomenon that even thoughthe Cu-rich phases are densely generated, the magnetization decreases.The cause of the decrease in magnetization seems to relate to that thedense generation of the Cu-rich phases results in a decrease in ratio ofthe Th₂Zn₁₇ crystal phase being the cell phase. The Th₂Zn₁₇ crystalphase is a phase responsible for magnetization in the Sm—Co-basedpermanent magnet, and a decrease in volume fraction of the Th₂Zn₁₇crystal phase is considered to cause a decrease in magnetization.

After close examination of the cause of there being a case where thesquareness ratio is improved and a case where it is not improved eventhrough the Cu-rich phases are densely creased, it has been found thatthe Cu-rich phase has characteristics in generation form. Morespecifically, it has been found that the Cu-rich phases intersect orcome into contact with each other and thereby improve the squarenessratio. On the other hand, a sample, which is not excellent in squarenessratio even if the Cu-rich phases are densely creased, has fewer pointswhere the Cu-rich phases intersect or come into contact with each other.

The difference in squareness ratio due to the difference in thegeneration form of the Cu-rich phase means the difference indisplacement of the domain wall due to the difference in structure. Forexample, the Cu-rich phases intersecting or coming into contact witheach other and the Cu-rich phases surrounding the Th₂Zn₁₇ crystal phasemakes it possible to increase the effect of suppressing the domain walldisplacement. On the other hand, when the Cu-rich phases do notintersect or come into contact with each other, the domain wall isdisplaced by slipping between the plurality of Cu-rich phases even ifthey are densely generated, resulting in a decreased squareness ratio.Further, the Cu concentration at the intersection of the Cu-rich phasesis sometimes higher than the Cu concentration in the other region of theCu-rich phase, and the intersection itself is considered to become astrong pinning site.

The permanent magnet in this embodiment has an intersection of theCu-rich phases. Concretely, in the cross section including the c-axis ofthe Th₂Zn₁₇ crystal phase, the number of intersections of the Cu-richphases existing in an area of 1 μm square is set 10 or more, and thenumber of intersections of the Cu-rich phases existing in an area of 500nm square is preferably set to 15 or more. Note that the upper limit ofthe number of intersections of the Cu-rich phases is not particularlylimited, but may be set to, for example, 120 or less.

In an actual sample, the intersection of the Cu-rich phases isrecognized as follows for instance.

First, in the mapping result in FIG. 2, a circle of a diameter of 100 nmis drawn around a point which is considered to be an intersection of theCu-rich phases. Next, the Cu-rich phases in the circle of the diameterof 100 nm are visually found. In this event, when two or more Cu-richphases having longitudinal directions extending in different directionsexist in the circle of the diameter of 100 nm and the two or moreCu-rich phases are in contact or intersect with each other, the contactpoint or the intersection is recognized as the intersection of theCu-rich phases.

Further, not limited to the above, even when two or more Cu-rich phasesare not in contact or does not intersect with each other, for example,if two or more Cu-rich phases having longitudinal directions are not inparallel and, when at least one of the two or more Cu-rich phases isextended in the longitudinal direction, the two or more Cu-rich phasesare in contact or intersect with each other in the circle, the contactpoint or the intersection generated when it is extended is recognized asthe intersection of the Cu-rich phases.

Further, the number of intersections of the Cu-rich phases is counted asfollows.

First, the number of intersections of the Cu-rich phases is counted inan area of 1 μm square at an arbitrary observation position in thesample. The above operation is performed at seven fields of view withthe observation position changed in the same sample, and an average offive results except the result of the maximum number of intersectionsand the minimum number of intersections is regarded as the number ofintersections of the Cu-rich phases existing in the area of 1 μm square.

Note that the squareness ratio is defined as follows. First, a DCmagnetizing property at room temperature is measured by a DC B-H tracer.Next, from a B-H curve obtained by the measurement result, a residualmagnetization M_(r), a coercive force _(i)Hc, and a maximum energyproduct (BH)max which are basic magnet properties of the magnet arefound. In this event, a theoretical maximum value (BH)max is obtainedusing Mr by the following formula (1).

(BH)max(theoretical value)=M _(r) ²/4μ₀  (1)

The squareness ratio is evaluated by a ratio between (BH)max obtained bythe measurement and (BH)max (theoretical value) and can be obtained bythe following formula (2).

(BH)max(actual measured value)/(BH)max(theoretical value)×100  (2)

Note that the permanent magnet in this embodiment is used, for example,also as a bond magnet. For example, using the magnet material in thisembodiment for a variable magnet in a variable magnetic flux drivesystem as disclosed in JP-A No. 2008-29148 or JP-A No. 2008-43172,enables increased efficiency, downsizing, and cost reduction of thesystem. For using the magnet material in this embodiment for a variablemagnet, it is necessary to change the aging treatment condition to keepthe coercive force within 100 kA/M or more and 350 kA/M or less.

<Manufacturing Method of Permanent Magnet>

Next, an example of a manufacturing method of a permanent magnet will bedescribed.

First, an alloy powder containing predetermined elements necessary forsynthesis of the permanent magnet is prepared. The alloy powder can beprepared, for example, by fabricating an alloy thin strip in a flakeform by a strip cast method and thereafter grindingthe alloy thin strip.In the fabrication of the alloy thin strip using the strip cast method,by tiltingly injecting an alloy molten metal to a chill roll rotating ata circumferential speed of 0.1 m/sec or more and 20 m/sec or less, acontinuously solidified thin strip with a thickness of 1 mm or less canbe fabricated. When the circumferential speed is less than 0.1 m/sec, acomposition variation is likely to occur in the thin strip. On the otherhand, when the circumferential speed is over 20 m/sec, crystal grainsbecome fine to a single domain size or less, and therefore the magneticproperty may decrease. The circumferential speed of the chill roll is0.3 m/sec or more and 15 m/sec or less, and more preferably 0.5 m/sec ormore and 12 m/sec or less. Further, the alloy powder can be preparedalso by grinding an alloy ingot obtained by casting after arc melting orhigh-frequency melting. Furthermore, the alloy powder may be preparedusing a mechanical alloying method, a mechanical grinding method, a gasatomizing method, a reduction diffusion method, or the like.

Further, performing a heat treatment on the alloy powder or a materialof an alloy before grinding makes it possible to homogenize thematerial. The material can be ground using, for example, a jet mill, aball mill or the like. Note that grinding the material in an inert gasatmosphere or an organic solvent makes it possible to prevent oxidationof the powder.

The powder obtained after the grinding has an average grain size of 2 μmor more and 5 μm or less and has a ratio of powder having a grain sizeof 2 μm or more and 10 μm or less of 80% or more of the whole powder, ishigh in degree of orientation and in coercive force. To realize such apowder, grinding by the jet mill is preferable.

For example, in the case of grinding by the ball mill, even if theaverage grain size of the powder is 2 μm or more and 5 μm or less, alarge amount of fine powder having a grain size on a sub-micron level iscontained. When the fine powder aggregates, the c-axes of crystals in aTbCu₇ crystal phase become unlikely to align in a direction of easymagnetization axis during magnetic field orientation at the time ofpress-forming, and the degree of orientation is likely to deteriorate.Further, such a fine powder may increase the amount of the oxide in thesintered compact to decrease the coercive force. In particular, when theFe concentration is 23 at % or more, the ratio of powder having a grainsize of 10 μm or more in the powder after the grinding is preferably 10%or less of the whole powder. When the Fe concentration is 23 at % ormore, the amount of the hetero-phase in the ingot being a raw materialincreases. In the hetero-phase, not only the amount of powder increasesbut also the grain size tends to increase, and the grain size sometimesbecomes 20 μm or more.

At the time of grinding such an ingot, for example, powder having agrain size of 15 μm or more sometimes becomes a hetero-phase powder asit is. When the ground powder containing such a hetero-phase coarsepowder is pressed in a magnetic field into a sintered compact, thehetero-phase remains to cause decrease in coercive force, decrease inmagnetization, and decrease in squareness. The decrease in thesquareness makes the magnetization difficult. In particular,magnetization after assembly to the rotor or the like becomes difficult.As described above, setting the powder having a grain size of 10 μm ormore to 10% or less of the whole makes it possible to increase thecoercive force while suppressing the decrease in squareness ratio in thehigh Fe concentration composition containing 23 at % or more Fe.

Next, the alloy powder is filled in a mold placed in an electromagnetand is press-formed while a magnetic field is applied thereto, whereby agreen compact whose crystal axes are oriented is manufactured. Bysintering the green compact at 1100° C. or higher and 1210° C. or lowerfor 1 hour or more and 15 hours or less, a dense sintered compact isobtained.

For example, when the sintering temperature is lower than 1100° C., thedensity of the sintered compact to be generated is likely to lower. Onthe other hand, when the sintering temperature is higher than 1210° C.,Sm in the powder excessively evaporates and thereby may decrease themagnetic property. The sintering temperature is more preferably 1150° C.or higher and 1205° C. or lower, and still more preferably 1165° C. orhigher and 1195° C. or lower.

On the other hand, when the sintering time is less than 1 hour, thedensity is likely to become uneven and therefore the magnetization islikely to decrease, further the crystal grain size of the sinteredcompact decreases, the crystal grain boundary ratio increases, andtherefore the magnetization is likely to decrease. On the other hand,when the sintering time is over 15 hours, the element R in the powderexcessively evaporates and thereby may decrease the magnetic property.The sintering time is more preferably 2 hours or more and 13 hours orless, and still more preferably 4 hours or more and 10 hours or less.Note that performing a heat treatment in a vacuum or an argon gas (Ar)makes it possible to suppress oxidation. Further, a vacuum is kept untilthe temperature becomes close to the sintering temperature andthereafter the atmosphere is changed to an Ar atmosphere and isothermalretention is performed, thereby aking it possible to increase thesintered compact density.

Next, a solution treatment is applied to the obtained sintered compactto control its crystal structure. For example, the solution treatment isperformed at 1100° C. or higher and 1190° C. or lower for 3 hours ormore and 28 hours or less, whereby the TbCu₇ crystal phase being theprecursor of the phase separation structure is easily obtained.

When the heat treatment temperature is lower than 1100° C. or is over1190° C., the ratio of the TbCu₇ crystal phase existing in the sampleafter the solution treatment is small and a good magnetic property isless likely to be achieved. The heat treatment temperature is preferably1110° C. or higher and 1180° C. or lower, and more preferably 1120° C.to 1170° C.

When the heat treatment time is less than 3 hours, the constituentphases are likely to become uneven, the coercive force becomes likely todecrease, the crystal grain size of the sintered compact is likely todecrease, the crystal grain boundary ratio increases, and themagnetization is likely to decrease. On the other hand, when the heattreatment time is over 28 hours, the element R in the sintered compactevaporates and thereby may decrease the magnetic property. The heattreatment time is preferably 4 hours or more and 24 hours or less, andmore preferably 10 hours or more and 18 hours or less.

Note that performing the solution treatment in a vacuum or an insertatmosphere such as an argon gas (Ar) makes it possible to suppressoxidation of the powder. Further, the solution treatment may beperformed following the sintering.

Further, the rapid cooling is performed after the isothermal retention.Performing the rapid cooling makes it possible to keep the TbCu₇ crystalphase even at room temperature. Setting the rapid cooling rate to 170°C./min or more makes it possible to stabilize the TbCu₇ crystal phase tocause a coercive force to be easily exhibited. For example, the rapidcooling rate is lower than 170° C./min, a Ce₂Ni₇ crystal phase (2-7phase) is likely to be generated during the cooling. The existence ofthe 2-7 phase may decrease the magnetization and may also decrease thecoercive force. This is because the 2-7 phase has often been thickened,so that the Cu concentration in the main phase decreases to makeoccurrence of the phase separation by the aging treatment difficult. Inparticular, in the composition containing 23 at % or more Fe, thecooling rate is likely to be important.

Next, the sintered compact after the rapid cooling is subjected to anaging treatment. The aging treatment means a treatment of enhancing thecoercive force of the magnet by controlling the metal structure, and isintended to phase-separate the metal structure of the magnet into aplurality of phases such as the Th₂Zn₁₇ crystal phase, the Cu-rich phaseand so on. The aging treatment here can be divided into a preliminaryaging treatment and a main aging treatment. For example, in thepreliminary aging treatment, the sintered compact is retained at 550° C.or higher and 850° C. or lower for 0.5 hours or more and 10 hours orless, and then gradually cooled to 200° C. or higher and 450° C. orlower at a cooling rate of 0.2° C./min or more and 5° C./min or less.

Setting a preliminary aging treatment temperature lower than a mainaging treatment temperature by a fixed temperature or more, makes itpossible to increase the nucleation frequency of the Cu-rich phase andincrease the number of intersections of the Cu-rich phases, therebyimproving the squareness ratio. Note that when the preliminary agingtreatment temperature is lower than 550° C., the density of the Cu-richphase increases, the volume fraction of the Cu-rich phase increases, andthe Cu concentration in each Cu-rich phase decreases. This converselydecreases the domain wall pinning effect, the coercive force hardlyincreases even if the main aging treatment is performed thereafter, anddeterioration in squareness ratio, decrease in magnetization and thelike may occur. A diffusion behavior of the element is considered to beinvolved therein. For example, when the volume fraction of the Cu-richphase increases, the volume fraction of the Th₂Zn₁₇ crystal phase beingthe phase responsible for magnetization decreases, resulting in decreasein magnetization. Further, when the preliminary aging treatmenttemperature becomes higher than 850° C., the squareness ratioimprovement effect may decrease. The preliminary aging treatmenttemperature is more preferably 550° C. or higher and 750° C. or lower,and still more preferably 600° C. or higher and 710° C. or lower.

Further, in the above aging treatment, attention should be paid to therelation between the preliminary aging treatment temperature and themain aging treatment temperature. Decreasing the preliminary agingtreatment temperature further improves the squareness ratio but makes itdifficult to increase the coercive force. A conceivable cause of thedecrease in coercive force is insufficient formation of the cell wallphase by the main aging treatment. Hence, in this embodiment, the mainaging treatment temperature is increased to promote the elementdiffusion. Concretely, the difference between the preliminary agingtreatment temperature and the main aging treatment temperature is set to130° C. or more. This makes it possible to, even in a compositioncontaining 23 at % or more Fe, increase the Cu concentration in theCu-rich phase while increasing the number of intersections of theCu-rich phases. For example, it is possible to set the number ofintersections of the Cu-rich phases existing in an area of 1 μm squareto 10 or more, more preferably 15 or more, and still more preferably 20or more. Accordingly, an excellent squareness ratio, a high coerciveforce, and high magnetization can be realized at the same time. Thedifference between the preliminary aging treatment temperature and themain aging treatment temperature is preferably 130° C. or more and 250°C. or less, and more preferably 135° C. or more and 180° C. or less.

Further, in the main aging treatment, the sintered compact is retainedat 750° C. or higher and 880° C. or lower for 2 hours or more and 80hours or less, and then gradually cooled to 300° C. or higher and 650°C. or lower at a cooling rate of 0.2° C./min or more and 2° C./min orless. In this event, by retaining the sintered compact at 300° C. orhigher and 650° C. or lower for a fixed time, the coercive force canalso be improved. The retention time in this event is preferably 1 houror more and 6 hours or less.

Note that by performing the preliminary aging treatment and the mainaging treatment in a vacuum or an insert gas such as an argon gas,oxidation of the sintered compact can be suppressed.

With the above, a permanent magnet can be manufactured.

Second Embodiment

The permanent magnet in the first embodiment can be used for variousmotors and power generators, and can also be used as a stationary magnetor a variable magnet of variable magnetic flux motors and variablemagnetic flux power generators. The permanent magnet in the firstembodiment is used to constitute various motors and power generators.When the permanent magnet in the first embodiment is applied to thevariable magnetic flux motor, techniques disclosed in JP-A No.2008-29148 and JP-A No. 2008-43172 are applicable to the configurationand drive system of the variable magnetic flux motor.

Next, a motor and a power generator including the permanent magnet inthis embodiment will be described referring to the drawings. FIG. 3 is aview illustrating a permanent magnet motor in this embodiment. In apermanent magnet motor 1 illustrated in FIG. 3, a rotor 3 is arranged ina stator 2. In an iron core 4 of the rotor 3, permanent magnets 5 beingthe permanent magnets in the first embodiment are arranged. Using thepermanent magnets in the first embodiment enables increased efficiency,downsizing, and cost reduction and so on, on the basis of the propertiesand so on of the permanent magnets.

FIG. 4 is a view illustrating a variable magnetic flux motor accordingto this embodiment. In a variable magnetic flux motor 11 illustrated inFIG. 4, a rotor 13 is disposed in a stator 12. In an iron core 14 of therotor 13, the permanent magnets in the first embodiment are disposed asstationary magnets 15 and variable magnets 16. The magnetic flux density(flux quantum) of the variable magnet 16 can be variable. The variablemagnet 16 is not influenced by a Q-axis current because itsmagnetization direction is perpendicular to a Q-axis direction, and canbe magnetized by a D-axis current. In the rotor 13, a magnetizationwinding (not illustrated) is provided. When a current is passed throughthe magnetization winding from a magnetizing circuit, its magnetic fieldacts directly on the variable magnets 16.

According to the permanent magnet in the first embodiment, a coerciveforce suitable for the stationary magnet 15 can be obtained. When thepermanent magnet in the first embodiment is applied to the variablemagnet 16, it is only necessary to control the coercive force, forexample, to a range of 100 kA/m or more and 500 kA/m or less by changingthe various conditions (aging treatment condition and so on) of theaforesaid manufacturing method. Note that in the variable magnetic fluxmotor 11 illustrated in FIG. 4, the permanent magnet in the firstembodiment is usable as both of the stationary magnet 15 and thevariable magnet 16, and the permanent magnet in the first embodiment maybe used as either one of the magnets. The variable magnetic flux motor11 is capable of outputting large torque with a small device size andthus is suitable for motors of hybrid vehicles, electric vehicles andthe like whose motors are required to have a high output and a smallsize.

FIG. 5 illustrates a power generator according to this embodiment. Apower generator 21 illustrated in FIG. 5 includes a stator 22 using thepermanent magnet in this embodiment. A rotor 23 disposed inside thestator 22 is connected via a shaft 25 to a turbine 24 provided at oneend of the power generator 21. The turbine 24 rotates by an externallysupplied fluid for instance. Instead of the turbine 24 rotating by thefluid, the shaft 25 can also be rotated by transmitting dynamic rotationsuch as regenerative energy of a vehicle. As the stator 22 and the rotor23, various publicly known structures are adoptable.

The shaft 25 is in contact with a commutator (not illustrated) disposedopposite the turbine 24 with respect to the rotor 23, so that anelectromotive force generated by the rotation of the rotor 23 is boostedto a system voltage and transmitted as an output of the power generator21 via an isolated phase bus and a traction transformer (notillustrated). The power generator 21 may be either of an ordinary powergenerator and a variable magnetic flux power generator. Note that therotor 23 is electrically charged due to static electricity from theturbine 2 and a shaft current accompanying the power generation.Therefore, the power generator 21 includes a brush 26 for dischargingthe charged electricity of the rotor 23.

As described above, applying the permanent magnet in the firstembodiment to the power generator provides effects such as increasedefficiency, downsizing, cost reduction and so on.

While certain embodiments of the present invention have been described,these embodiments have been presented by way of example only, and arenot intended to limit the scope of the inventions. Indeed, the novelembodiments described herein may be embodied in a variety of otherforms; furthermore, various omissions, substitutions and changes may bemade without departing from the spirit of the inventions. Theseembodiments and their modifications fall within the scope and spirit ofthe inventions and fall within the scope of the inventions described inclaims and their equivalents.

EXAMPLES

In examples, concrete examples of the permanent magnet will bedescribed.

Example 1 and Example 2

Respective raw materials to be used for the permanent magnet wereweighed and mixed at predetermined ratios and were then subjected toarc-melting in an Ar gas atmosphere, whereby alloy ingots werefabricated. The alloy ingots were retained at 1175° C. for 10 hours andthereby subjected to a heat treatment, and the alloy ingots were thencoarsely ground and ground by a jet mill, whereby alloy powders as rawmaterial powders of magnets were prepared. The alloy powders werepress-formed in a magnetic field, whereby compression-molded bodies werefabricated. Then, the compression-molded bodies of the alloy powderswere disposed in a chamber of a sintering furnace, the inside of thechamber was brought to a vacuum state and then raised up to 1180° C. andkept as it for 1 minute, then an Ar gas was led thereinto, thetemperature was raised up to 1195° C. in an Ar atmosphere, and thetemperature was kept for 4 hours for performing main sintering.

Subsequently to the main sintering step, the sintered compacts wereretained at 1160° C. for 10 hours and thereby subjected to a solutiontreatment. Note that the cooling rate after the solution treatment wasset to −220° C./min. Then, the sintered compacts after the solutiontreatment were retained at 670° C. for 2 hours as the preliminary agingtreatment and then gradually cooled to room temperature, and furtherretained at 815° C. for 40 hours as the main aging treatment. Thesintered compacts subjected to the aging treatment under such conditionswere gradually cooled to 420° C. and retained at the temperature for 1hour. Thereafter, the sintered compacts were furnace-cooled to roomtemperature, whereby magnets were obtained. The compositions of theobtained magnets are as listed in Table 1.

A composition analysis of the magnet was carried out by an inductivelycoupled plasma (ICP) method. Note that the composition analysis by theICP method was carried out in the following procedure. First, a samplepicked up from a described measurement point was ground in a mortar, apredetermined amount of the ground sample was weighed and put into aquartz beaker. Further, a mixed acid (acid containing nitric acid andhydrochloric acid) was put into the beaker and heated to about 140° C.on a hotplate, whereby the sample in the beaker was completely melted.It was left standing to cool, then transferred to a polyethyl acrylate(PEA) volumetric flask, and quantified to be a sample solution. Further,quantities of components of the sample solution were determined by acalibration curve method using an ICP emission spectrochemical analyzer.As the ICP emission spectrochemical analyzer, SPS4000 manufactured bySII Nano Technology Inc. was used. Further, the number of intersectionsof the Cu-rich phases existing in an area of 1 μm square (Cu-rich phaseintersection number), the Cu concentration in the Cu-rich phase (Cu-richphase Cu concentration), the squareness ratio, the coercive force, andthe residual magnetization of each of the magnets are listed in Table 3.

Example 3, Example 4, and Example 5

Respective raw materials were weighed and mixed at predetermined ratiosand then subjected to high-frequency melting in an Ar gas atmosphere,whereby alloy ingots were fabricated. The alloy ingots were coarselyground, then heat-treated at 1160° C. for 4 hours, and cooled to roomtemperature by rapid cooling. Further, they were coarsely ground andground by a jet mill, whereby alloy powders as raw material powders ofmagnets were prepared. Further, the alloy powders were press-formed in amagnetic field, whereby compression-molded bodies were fabricated.

Next, the compression-molded bodies of the alloy powders were disposedin a chamber of a sintering furnace, the inside of the chamber wasbrought to a vacuum state of a degree of vacuum of 9.0×10⁻³ Pa and thenraised up to 1170° C. and kept as it was for 5 minutes, and then an Argas was led into the chamber. The temperature inside the chamber broughtinto an Ar atmosphere was raised up to 1185° C., and kept as it was for6 hours for performing main sintering. Next, the sintered compacts wereretained at 1120° C. for 12 hours and thereby subjected to a solutiontreatment. Note that the cooling rate after the solution treatment wasset to −200° C./min.

Next, as listed in Table 2, the sintered compacts after the solutiontreatment were retained at 705° C. for 1 hour as the preliminary agingtreatment, and then gradually cooled to room temperature. The sinteredcompacts were then retained at 840° C. for 25 hours as the main agingtreatment, gradually cooled to 370° C. and retained for 2 hours, andthen furnace-cooled to room temperature, whereby magnets were obtained.The compositions of the magnets are as listed in Table 1. Note that thecompositions of the magnets were confirmed by the ICP method as in theother examples. Further, the Cu-rich phase intersection number, theCu-rich phase Cu concentration, the squareness ratio, the coerciveforce, and the residual magnetization of each of the magnets are listedin Table 3.

Example 6

Respective raw materials were weighed and mixed at predetermined ratiosand then subjected to high-frequency melting in an Ar gas atmosphere,whereby an alloy ingot was fabricated. The alloy ingot was coarselyground, then heat-treated at 1180° C. for 3 hours, and cooled to roomtemperature by rapid cooling. Further, it was coarsely ground and groundby a jet mill, whereby an alloy powder as a raw material powder of amagnet was prepared. Further, the alloy powder was press-formed in amagnetic field, whereby a compression-molded body was fabricated.

Next, the compression-molded body of the alloy powder was disposed in achamber of a sintering furnace, the inside of the chamber was brought toa vacuum state of a degree of vacuum of 9.0×10⁻³ Pa and then raised upto 1155° C. and kept as it was for 30 minutes, and then an Ar gas wasled into the chamber. The temperature inside the chamber brought into anAr atmosphere was raised up to 1190° C., and kept as it was for 3 hoursfor performing main sintering. Next, the sintered compact was retainedat 1130° C. for 16 hours and thereby subjected to a solution treatment.Note that the cooling rate after the solution treatment was set to −180°C./min.

Next, as listed in Table 2, the sintered compact after the solutiontreatment was retained at 700° C. for 1.5 hours as the preliminary agingtreatment, and then gradually cooled to room temperature. The sinteredcompact was then retained at 850° C. for 35 hours as the main agingtreatment, gradually cooled to 360° C. and retained as it was for 1.5hours, and then furnace-cooled to room temperature, whereby a magnet wasobtained. The composition of the obtained magnet is as listed inTable 1. Note that the composition of the magnet was confirmed by theICP method as in the other examples. Further, the Cu-rich phaseintersection number, the Cu-rich phase Cu concentration, the squarenessratio, the coercive force, and the residual magnetization of the magnetare listed in Table 3.

Example 7

Respective raw materials were weighed and mixed at predetermined ratiosand then subjected to high-frequency melting in an Ar gas atmosphere,whereby an alloy ingot was fabricated. The alloy ingot was coarselyground, then heat-treated at 1170° C. for 12 hours, and cooled to roomtemperature by rapid cooling. Further, it was coarsely ground and groundby a jet mill, whereby an alloy powder as a raw material powder of amagnet was prepared. Further, the alloy powder was press-formed in amagnetic field, whereby a compression-molded body was fabricated.

Next, the compression-molded body of the alloy powder was disposed in achamber of a sintering furnace, the inside of the chamber was brought toa vacuum state of a degree of vacuum of 9.0×10⁻³ Pa and then raised upto 1155° C. and kept as it was for 30 minutes, and then an Ar gas wasled into the chamber. The temperature inside the chamber brought into anAr atmosphere was raised up to 1180° C., and kept as it was for 10 hoursfor performing main sintering. Next, the sintered compact was retainedat 1120° C. for 16 hours and thereby subjected to a solution treatment.Note that the cooling rate after the solution treatment was set to −240°C./min.

Next, as listed in Table 2, the sintered compact after the solutiontreatment was retained at 680° C. for 3 hours as the preliminary agingtreatment, and then gradually cooled to room temperature. The sinteredcompact was then retained at 820° C. for 50 hours as the main agingtreatment, gradually cooled to 400° C. and retained as it was for 2hours, and then furnace-cooled to room temperature, whereby a magnet wasobtained. The composition of the obtained magnet is as listed inTable 1. Note that the composition of the magnet was confirmed by theICP method as in the other examples. Further, the Cu-rich phaseintersection number, the Cu-rich phase Cu concentration, the squarenessratio, the coercive force, and the residual magnetization of the magnetare listed in Table 3.

Example 8

Respective raw materials were weighed and mixed at predetermined ratiosand then subjected to high-frequency melting in an Ar gas atmosphere,whereby an alloy ingot was fabricated. The alloy ingot was coarselyground, then heat-treated at 1170° C. for 6 hours, and cooled to roomtemperature by rapid cooling. Further, it was coarsely ground and groundby a jet mill, whereby an alloy powder as a raw material powder of amagnet was prepared. Further, the alloy powder was press-formed in amagnetic field, whereby a compression-molded body was fabricated.

Next, the compression-molded body of the alloy powder was disposed in achamber of a sintering furnace, the inside of the chamber was brought toa vacuum state of a degree of vacuum of 9.0×10⁻³ Pa and then raised upto 1165° C. and kept as it was for 15 minutes, and then an Ar gas wasled into the chamber. The temperature inside the chamber brought into anAr atmosphere was raised up to 1195° C., and kept as it was for 4 hoursfor performing main sintering. Next, the sintered compact was retainedat 1125° C. for 12 hours and thereby subjected to a solution treatment.Note that the cooling rate after the solution treatment was set to −180°C. min.

Next, as listed in Table 2, the sintered compact after the solutiontreatment was retained at 675° C. for 4 hours as the preliminary agingtreatment, and then gradually cooled to room temperature. The sinteredcompact was then retained at 830° C. for 35 hours as the main agingtreatment, gradually cooled to 350° C. and retained as it was for 2hours, and then furnace-cooled to room temperature, whereby a magnet wasobtained. The composition of the obtained magnet is as listed inTable 1. Note that the composition of the magnet was confirmed by theICP method as in the other examples. Further, the Cu-rich phaseintersection number, the Cu-rich phase Cu concentration, the squarenessratio, the coercive force, and the residual magnetization of the magnetare listed in Table 3.

Example 9, Example 10, and Example 11

Alloy powders having the same composition as that of Example 8 were usedas raw materials and press-formed in a magnetic field, wherebycompression-molded bodies were fabricated. The compression-molded bodieswere disposed in a chamber of a sintering furnace, the inside of thechamber was brought to a vacuum state of a degree of vacuum of 9.0×10⁻³Pa and then raised up to 1165° C. and kept as it was for 15 minutes, andthen an Ar gas was led into the chamber. The temperature inside thechamber brought into an Ar atmosphere was raised up to 1195° C., andkept as it was for 4 hours for performing main sintering.

Next, a solution treatment was carried out under the same conditions asthose of Example 8. Further, as listed in Table 2, the sintered compactwas retained at 700° C. for 4 hours as the preliminary aging treatmentand then gradually cooled to room temperature in Example 9, the sinteredcompact was retained at 670° C. for 4 hours as the preliminary agingtreatment and then gradually cooled to room temperature in Example 10,and the sintered compact was retained at 675° C. for 4 hours as thepreliminary aging treatment and then gradually cooled to roomtemperature in Example 11. The sintered compacts were then retained at830° C. for 35 hours as the main aging treatment, gradually cooled to350° C. and retained as they were for 2 hours, and then furnace-cooledto room temperature, whereby magnets were obtained. The compositions ofthe obtained magnets are as listed in Table 1. Note that thecompositions of the magnets were confirmed by the ICP method as in theother examples. Further, the Cu-rich phase intersection number, theCu-rich phase Cu concentration, the squareness ratio, the coerciveforce, and the residual magnetization of each of the magnets are listedin Table 3.

Comparative Example 1 and Comparative Example 2

Magnets having the compositions listed in Table 1 were fabricated by thesame methods as those of Example 1 and Example 2, respectively. TheCu-rich phase intersection number, the Cu-rich phase Cu concentration,the squareness ratio, the coercive force, and the residual magnetizationof each of the magnets are listed in Table 3.

Comparative Example 3, Comparative Example 4, Comparative Example 5, andComparative Example 6

Alloy powders having the same composition as that of Example 8 were usedas raw materials and press-formed in a magnetic field, wherebycompression-molded bodies were fabricated. The compression-molded bodieswere disposed in a chamber of a sintering furnace, the inside of thechamber was brought to a vacuum state of a degree of vacuum of 9.0×10⁻³Pa and then raised up to 1165° C. and kept as it was for 15 minutes, andthen an Ar gas was led into the chamber. The temperature inside thechamber brought into an Ar atmosphere was raised up to 1195° C., andkept as it was for 4 hours for performing main sintering. Next, asolution treatment was carried out under the same conditions as those ofExample 8.

Further, as listed in Table 2, in Comparative Example 3, the sinteredcompact was retained at 780° C. for 4 hours as the preliminary agingtreatment and then gradually cooled to room temperature, then retainedat 830° C. for 35 hours as the main aging treatment, gradually cooled to350° C. and retained as it was for 2 hours, and then furnace-cooled toroom temperature, whereby a magnet was obtained.

Further, as listed in Table 2, in Comparative Example 4, the sinteredcompact was retained at 675° C. for 4 hours as the preliminary agingtreatment and then gradually cooled to room temperature, then retainedat 900° C. for 35 hours as the main aging treatment, gradually cooled to350° C. and retained as it was for 2 hours, and then furnace-cooled toroom temperature, whereby a magnet was obtained.

Further, as listed in Table 2, in Comparative Example 5, the sinteredcompact was retained at 675° C. for 4 hours as the preliminary agingtreatment and then gradually cooled to room temperature, then retainedat 780° C. for 35 hours as the main aging treatment, gradually cooled to350° C. and retained as it was for 2 hours, and then furnace-cooled toroom temperature, whereby a magnet was obtained.

Further, as listed in Table 2, in Comparative Example 6, the sinteredcompact was retained at 450° C. for 4 hours as the preliminary agingtreatment and then gradually cooled to room temperature, then retainedat 830° C. for 35 hours as the main aging treatment, gradually cooled to350° C. and retained as it was for 2 hours, and then furnace-cooled toroom temperature, whereby a magnet was obtained.

The compositions of the magnets are as listed in Table 1. Note that thecompositions of the magnets were confirmed by the ICP method as in theother examples. Further, the Cu-rich phase intersection number, theCu-rich phase Cu concentration, the squareness ratio, the coerciveforce, and the residual magnetization of each of the magnets are listedin Table 3.

As is clear from Table 1 to Table 3, the permanent magnets in Example 1to Example 7 are higher in Cu concentration in the Cu-rich phase andlarger in the number of intersections of the Cu-rich phases than, forexample, the permanent magnet in Comparative Example 1 having an Smconcentration of 12.73% and the permanent magnet in Comparative Example2 having a Zr concentration of 4.84%, and thus each exhibit excellentsquareness ratio, high coercive force, and high magnetization. Thisshows that adjusting the amounts of elements constituting the permanentmagnet enables enhancement of the magnet property.

Further, the permanent magnets in Example 8 to Example 11 are larger inthe number of intersections of the Cu-rich phases than the permanentmagnet in Comparative Example 3 in which the preliminary aging treatmenttemperature is 780° C. and the temperature difference between thepreliminary aging treatment temperature and the main aging treatmenttemperature is 50° C., and thus each exhibit excellent squareness ratio,high coercive force, and high magnetization. This shows that controllingthe preliminary aging treatment temperature and the temperaturedifference between the preliminary aging treatment temperature and themain aging treatment temperature enables enhancement of the magnetproperty.

Further, the permanent magnets in Example 8 to Example 11 are larger inthe number of intersections of the Cu-rich phases than, for example, thepermanent magnet in Comparative Example 4 in which the main agingtreatment temperature is 900° C. and the temperature difference betweenthe preliminary aging treatment temperature and the main aging treatmenttemperature is 225° C., and thus each exhibit excellent squarenessratio, high coercive force, and high magnetization. This shows thatcontrolling the main aging treatment temperature and the temperaturedifference between the preliminary aging treatment temperature and themain aging treatment temperature enables enhancement of the magnetproperty.

Further, the permanent magnets in Example 8 to Example 11 are higher inCu concentration in the Cu-rich phase and larger in the number ofintersections of the Cu-rich phases than, for example, the permanentmagnet in Comparative Example 5 in which the main aging treatmenttemperature is 780° C. and the temperature difference between thepreliminary aging treatment temperature and the main aging treatmenttemperature is 105° C., and thus each exhibit excellent squarenessratio, high coercive force, and high magnetization. This shows thatcontrolling the main aging treatment temperature and the temperaturedifference between the preliminary aging treatment temperature and themain aging treatment temperature enables enhancement of the magnetproperty.

Further, the permanent magnets in Example 8 to Example 11 are higher inCu concentration in the Cu-rich phase than, for example, the permanentmagnet in Comparative Example 6 in which the preliminary aging treatmenttemperature is 450° C. and the temperature difference between thepreliminary aging treatment temperature and the main aging treatmenttemperature is 380° C., and thus each exhibit excellent squarenessratio, high coercive force, and high magnetization. This shows thatcontrolling the preliminary aging treatment temperature and thetemperature difference between the preliminary aging treatmenttemperature and the main aging treatment temperature enables enhancementof the magnet property.

As described above, the magnets in Example 1 to Example 11, in which theCu concentration in the Cu-rich phase is as high as 30% or more and thenumber of intersections of the Cu-rich phases is as large as 10 or more,each exhibit excellent squareness ratio, high coercive force, and highmagnetization even if the Fe concentration is 23% or more. This showsthat the permanent magnets in Example 1 to Example 11 are excellent inmagnet property.

TABLE 1 MAGNET COMPOSITION (ATOMIC RATIO) (Other: (Example) 1: Ce, 2:Ti, 3: Mn, 4: Cr 5: Al0.0115 + Cr0.015, (Comparative Example) 1: Cr, 2:Ti) Sm Co Fe Cu Zr Other Example 1 11.01 56.99 23.52 5.33 2.93 0.22Example 2 11.98 54.57 25.97 5.72 1.70 0.06 Example 3 10.81 53.16 29.085.17 1.43 0.35 Example 4 11.30 53.18 29.27 4.44 1.73 0.08 Example 510.99 50.02 28.04 9.08 1.69 0.18 Example 6 11.11 50.00 31.91 5.24 1.740.00 Example 7 11.24 47.80 34.17 5.24 1.55 0.00 Example 8 11.17 50.9030.91 5.33 1.69 0.00 Example 9 11.17 50.90 30.91 5.33 1.69 0.00 Example10 11.17 50.90 30.91 5.33 1.69 0.00 Example 11 11.17 50.90 30.91 5.331.69 0.00 Comparative 12.73 55.86 23.06 5.22 2.87 0.26 Example 1Comparative 11.98 51.42 25.97 5.72 4.84 0.07 Example 2 Comparative 11.1750.90 30.91 5.33 1.69 0.00 Example 3 Comparative 11.17 50.90 30.91 5.331.69 0.00 Example 4 Comparative 11.17 50.90 30.91 5.33 1.69 0.00 Example5 Comparative 11.17 50.90 30.91 5.33 1.69 0.00 Example 6

TABLE 2 Preliminary Main aging aging treatment treatment Temperaturetemperature temperature difference (° C.) (° C.) (° C.) Example 1 670815 145 Example 2 670 815 145 Example 3 705 840 135 Example 4 705 840135 Example 5 705 840 135 Example 6 700 850 150 Example 7 680 820 140Example 8 675 830 155 Example 9 700 830 130 Example 10 670 830 160Example 11 675 840 165 Comparative Example 1 670 815 145 ComparativeExample 2 670 815 145 Comparative Example 3 780 830 50 ComparativeExample 4 675 900 225 Comparative Example 5 675 780 105 ComparativeExample 6 450 830 380

TABLE 3 Cu rich Cu rich phase phase Cu Square- Coercive inter- concen-ness force Residual section tration ratio iHc magneti- number (mol %)(%) (kA/m) zation (T) Example 1 45 38 94.1 1610 1.145 Example 2 38 3692.9 1430 1.175 Example 3 29 41 91.5 1230 1.2 Example 4 30 30 90.6 11501.205 Example 5 24 52 90.8 1300 1.195 Example 6 19 39 90.1 1100 1.25Example 7 23 32 89.5 1050 1.26 Example 8 25 47 92.5 1380 1.24 Example 912 47 90.2 1410 1.245 Example 10 35 40 92.8 1320 1.24 Example 11 80 3493.4 1280 1.23 Comp. Exam. 1 7 10 65.5 220 1.145 Comp. Exam. 2 5 14 72.7340 1.17 Comp. Exam. 3 6 35 78.2 1400 1.18 Comp. Exam. 4 8 45 69.4 12801.15 Comp. Exam. 5 8 26 70.7 600 1.175 Comp. Exam. 6 108 22 84.5 8001.19

What is claimed is:
 1. A permanent magnet comprising: a compositionexpressed by a composition formula:R_(p)Fe_(q)M_(r)Cu_(t)Co_(100-p-q-r-t) where, R is at least one elementselected from the group consisting of rare-earth elements, M is at leastone element selected from the group consisting of Zr, Ti, and Hf, p is anumber satisfying 10.5≦p≦12.5 at %, q is a number satisfying 23≦q≦40 at%, r is a number satisfying 0.88≦r≦4.5 at %, and t is a numbersatisfying 4.5≦t≦10.7 at %; and a metal structure containing a Th₂Zn₁₇crystal phase and a Cu-rich phase having a Cu concentration higher thanthat of the Th₂Zn₁₇ crystal phase, wherein a number of intersections ofthe Cu-rich phases existing in an area of 1 μm square in a cross sectionincluding a c-axis of the Th₂Zn₁₇ crystal phase is 10 or more.
 2. Thepermanent magnet of claim 1, wherein the number of intersections is 120or less.
 3. The permanent magnet of claim 1, wherein the Cuconcentration in the Cu-rich phase is 30 at % or more.
 4. The permanentmagnet of claim 1, wherein 50 at % or more of a total amount of theelement R in the composition formula is Sm.
 5. The permanent magnet ofclaim 1, wherein 50 at % or more of the element M in the compositionformula is Zr.
 6. The permanent magnet of claim 1, wherein 20 at % orless of Co in the composition formula is substituted by at least oneelement selected from among Ni, V, Cr, Mn, Al, Ga, Nb, Ta, and W.
 7. Amotor comprising the permanent magnet of claim
 1. 8. A power generatorcomprising the permanent magnet of claim 1.